The invention relates to image-based virtual world environments.
Image data is commonly used to represent the real world. Unlike traditional geometry-based systems, there has been increased interest in developing high quality image-based systems for constructing virtual worlds. Image-based systems have the advantage of producing vivid and photo-realistic outputs using personal computers. Another advantage is that the cost of interactively displaying a scene is independent of the scene's complexity. In such systems, a series of images are first acquired by horizontally or vertically rotating a camera about its optical center. Then, the images are warped and stitched together, thereby constructing a panoramic environment map view of the real world.
Panoramic environment maps can be used in different applications such as movie special effects, virtual reality, or games. One problem with constructing such panoramic images relates to the method of stitching together different pieces of a scene to form a larger picture. One solution is to manually establish a relationship between the individual images and solve the unknown parameters of their relative transformations. However, such manual approaches are tedious for large applications.
There are a variety of different forms of environment maps used to render a virtual world. One common approach is to project the input images into a spherical environment map. There are two difficulties in spherical projection systems. One difficulty relates to the lack of a suitable representation for storage on a computer. The other difficulty relates to the placement of the camera. Unless the camera is positioned accurately, significant distortion between partially overlapped images occurs, leading to poor image registration. For these reasons, cylindrical mapping systems are often used to build virtual environment maps.
Referring to FIG. 2, the geometry for a cylindrical mapping system is illustrated. An image plane 10, represented by rectangular area PQRS is projected onto a hypothetical cylinder 12 represented by rectangular area pqrs and having an optical center O. Image plane 10 is tangent to cylinder 12 and has a center O', a focal length f and a radius d of the cylinder. Assume P(x,y) is a pixel in the image plane and p(u,v) is its corresponding pixel in the cylindrical map. From FIG. 2, the coordinates (u,v) can be obtained as follows: ##EQU1## and ##EQU2## Because, in this embodiment, radius d is equal to f, Equations (1) and (2) can be rewritten as follows: EQU u=f tan.sup.-1 x/f, (3)
and ##EQU3## Using Equations (3) and (4), the input images can be warped and then registered for constructing a complete circular panoramic scene.